A silicone aerosol type coating for waterproofing precision instruments and a method for preparing the same

Abstract

This invention belongs to the field of micro-coating protection and discloses an organosilicon aerosol coating for waterproofing precision instruments and its preparation method. The organosilicon aerosol coating comprises, by weight, 4-6 parts of fluorinated organosilicon, 2-3 parts of organosilicon-acrylate resin, 30-40 parts of a first solvent, 20-30 parts of a second solvent, 1-1.5 parts of a release agent, 0.5-1 parts of a leveling agent, and a certain amount of propellant. This invention uses a first solvent and a second solvent with different volatility properties to improve the self-leveling and film-forming quality of the microfilm after spraying, reducing surface micropore defects caused by excessive evaporation and forming a good waterproof layer. Through the synergistic effect of fluorinated organosilicon and organosilicon-acrylate resin as film-forming materials, the waterproof coating formed with the release agent and leveling agent possesses both long-lasting waterproofing and peelability. When used for the protection of precision instruments, the coating can be peeled off after a certain protection period without leaving residual pollution on the instrument surface.

Description

Technical Field

[0001] This invention belongs to the field of micro-coating protection, specifically relating to an organosilicon aerosol coating for waterproofing precision instruments and its preparation method. Background Technology

[0002] Electronic equipment, electrical equipment, precision components, and precision instruments exposed to humid environments for extended periods are highly susceptible to damage from moisture and corrosive gases. This is especially true in coastal areas with their high humidity and salt spray corrosion, where precision instruments are prone to moisture damage and rust due to high humidity, salt spray, and temperature condensation, severely impacting their accuracy and lifespan.

[0003] For precision instruments in fields such as drones, medical equipment, and testing instruments, daily moisture and water protection is extremely important. Current methods mainly involve applying silicone gel or placing silica gel desiccants. However, applying silicone gel to instruments is extremely inconvenient, making it difficult to precisely control the coating area, which affects the use of the instrument. In addition, silicone gel has a slight stickiness that can attract dust, causing dust accumulation and contamination of the instrument. Silica gel desiccants are external absorbent and need to be replaced frequently, which cannot meet the long-term waterproof and moisture-proof requirements of instruments.

[0004] On the other hand, various precision instruments equipped with intelligent control circuit boards, chips, and components are highly susceptible to damage from moisture, condensation, and salt spray, placing more stringent demands on moisture protection. Traditional waterproofing and moisture-proofing technologies are no longer sufficient. Therefore, the development of hydrophobic and waterproof micro-coatings using organosilicon has led to the prevention of corrosion from moisture and salt spray on equipment and instruments. Chinese Patent Publication No. CN104530967B discloses a reactive organosilicon waterproofing agent, its preparation method, and its application. It uses reactive MDTQ silicone resin as the base raw material, and combines it with polymethylsiloxane containing reactive silicon functional groups or its modified form, along with a room-temperature curing catalyst, in an organic solvent. The reactive organosilicon waterproofing agent is then prepared through chemical and physical methods. This organosilicon waterproofing agent can be sprayed onto substrates requiring waterproofing.

[0005] However, for the protection of precision instruments, it is not only required that a uniform and transparent micro-waterproof coating be formed after spraying, but also that the micro-coating, after film formation, does not affect the appearance of the precision instrument. Furthermore, the waterproof micro-coating should be peelable and removable after protection, without causing contamination to the surface of the precision instrument. For example, Chinese Patent Publication No. CN103923537B discloses a peelable protective coating spray and its production process, using fluororubber powder and polyester resin as film-forming materials. The peelable protective coating spray has good physical and chemical resistance, providing waterproofing, oil resistance, scratch resistance, and impact resistance. The protective film can be completely peeled off without damaging the substrate or leaving any marks. Chinese Patent Publication No. CN118206923B discloses a method for preparing a high-strength silicone peelable coating, using trisiloxane-phosphorus oxysilane, graphene-modified siloxane, phenyltrimethoxysilane, etc., as raw materials. After hydrolysis and condensation reactions, modified silicone is obtained, and finally, a peeling agent is added to the modified silicone to obtain a high-strength silicone peelable coating. Summary of the Invention

[0006] The purpose of this invention is to develop a silicone aerosol coating for waterproofing and moisture-proofing the surfaces of precision instruments. This coating, sprayed onto the surface of precision instruments, forms a transparent silicone waterproof coating for protection without affecting the appearance of the instruments. After a certain period of protection, the waterproof coating can be peeled off without leaving any residue on the surface. To this end, a silicone aerosol coating for waterproofing precision instruments is proposed. Utilizing condensation film formation and solvent evaporation film formation, and in conjunction with solvents of different volatility levels and a peeling aid, it is sprayed as an aerosol to rapidly form a uniform, micron-thick, transparent waterproof coating on the surfaces of precision instruments, circuit boards, etc. The coating has long-lasting waterproof properties and can be peeled off without affecting the surface of the instrument.

[0007] This invention is achieved through the following technical solution: An organosilicon aerosol coating for waterproofing precision instruments comprises, by weight: 4-6 parts fluorinated organosilicon, 2-3 parts organosilicon-acrylate resin, 30-40 parts first solvent, 20-30 parts second solvent, 1-1.5 parts release agent, 0.5-1 part leveling agent, and a certain amount of propellant; wherein: The fluorinated organosilicon is at least one of trifluoropropylmethyldimethoxysilane, tridecylfluorooctyltriethoxysilane, tridecylfluorooctyltrimethoxysilane, and heptadecafluorooctyltrimethoxysilane; The organosilicon-acrylate resin is obtained by polymerizing vinyl-terminated polydimethylsiloxane with acrylate; The first solvent is one of methyl ethyl ketone, ethyl acetate, and acetone; The second solvent is one of acetylacetone, butanol, or isopropanol; The stripping agent is silane coupling agent modified nano-silica; The leveling agent is an organosilicon polyether copolymer.

[0008] In a preferred embodiment of this invention, fluorinated organosilicon and organosilicon-acrylate resin are synergistically dissolved in a first solvent and a second solvent with different volatility characteristics. After the fluorinated organosilicon is dissolved, it is sprayed onto the surface of an instrument (suitable for materials such as carbon steel, stainless steel, titanium alloy, aluminum alloy, glass, and ceramics). As the highly volatile first solvent evaporates, the hydrolyzable groups in the silane molecules gradually hydrolyze upon contact with trace amounts of moisture in the air, further condensing to form a transparent, waterproof microfilm. The second solvent provides a more moderate volatility characteristic, allowing the dissolved organosilicon-acrylate resin to gradually self-level and form a film, reducing surface defects caused by excessively rapid evaporation, thereby forming a continuous, dense, and uniformly thick waterproof microcoating. When used in precision instruments, this protects the components from environmental corrosion such as moisture and salt spray, giving the instruments a good waterproof, stain-resistant, and self-cleaning surface.

[0009] In a preferred embodiment of the present invention, fluorinated organosilicon and organosilicon-acrylate resin are used synergistically. The fluorinated organosilicon forms a three-dimensional cross-linked network through a hydrolysis-condensation reaction, and the Si-OH groups therein can form hydrogen bonds or covalent bonds with the substrate surface, significantly improving adhesion and giving the coating long-lasting protection. The coating formed by the organosilicon-acrylate resin is flexible and peelable, ensuring that the protective coating does not contaminate the instrument surface.

[0010] In a preferred embodiment of the present invention, when ethyl acetate is used as the first solvent, butanol is used as the second solvent; that is, when the first solvent evaporates very quickly, a solvent with lower volatility is selected as the second solvent to better compensate for coating defects caused by rapid evaporation.

[0011] In a preferred embodiment of the present invention, the organosilicon-acrylate resin is obtained by free radical polymerization of vinyl-terminated polydimethylsiloxane and acrylate in a mass ratio of 3:4. The acrylate is at least one of methyl methacrylate and butyl acrylate. Organosilicon has low surface energy, and acrylate has film-forming properties. The organosilicon-acrylate resin formed by free radical polymerization combines low surface energy and self-cleaning effect, and possesses good chemical inertness, weather resistance, and water resistance.

[0012] Furthermore, the silicone-acrylate resin is obtained by ethyl radical copolymerization of vinyl-terminated polydimethylsiloxane and acrylate under the action of benzoyl peroxide as an initiator. A typical method for obtaining this resin is as follows: vinyl-terminated polydimethylsiloxane and acrylate are mixed in a mass ratio of 3:4, and benzoyl peroxide (2% of the total amount of vinyl-terminated polydimethylsiloxane and acrylate) is slowly added while stirring at 90-100°C. The copolymerization reaction is initiated and maintained at this temperature for 2-3 hours to obtain the silicone-acrylate resin. When making the resin in-house, the use of methyl methacrylate and butyl acrylate in combination yields better results. In particular, using more butyl acrylate results in a more flexible coating that is easier to peel off.

[0013] In a preferred embodiment of the present invention, the release agent is obtained by adding 3.5% by weight of γ-methacryloyloxypropyltrimethoxysilane (KH570) to nano-silica and stirring the mixture at 90-100°C for 3-5 hours. It forms a stable dispersion in organic solvents without significant sedimentation. In coatings, it imparts properties such as water resistance, oil resistance, and anti-fogging to the coating surface, making it easier to form a low-energy interface on the coating surface and increasing the coating release effect.

[0014] Furthermore, the nano-silica is selected from spherical nano-silica with a particle size of 10-100 nm. The regularly shaped spherical nano-silica serves as a structural modifier, dispersing in the coating to construct a micron-sized coating structure. This fills the micropores formed during film formation, resulting in a denser coating structure with weaker interfacial bonding. This effectively prevents water and salt ion penetration and increases the coating's peelability. In a preferred embodiment of the present invention, the silicone polyether copolymer is either DOWSIL™11 or DOWSIL™57. The silicone polyether copolymer promotes uniform leveling of the coating, increases the flexibility and integrity of the coating, regulates the low surface energy interface, and promotes the peelability of the coating.

[0015] In a preferred embodiment of the present invention, the propellant is at least one of HFC-134a, propane, and butane.

[0016] The present invention relates to a method for preparing an organosilicon aerosol coating for waterproofing precision instruments. The specific preparation method is as follows: (1) Dissolve the fluorinated organosilicon in the first solvent and stir evenly to obtain material 1; dissolve the organosilicon-acrylate resin in the second solvent and stir evenly to obtain material 2; mix material 1 and material 2, add peeling agent and leveling agent, ultrasonically disperse, filter, and obtain organosilicon waterproof coating; (2) The silicone waterproof coating is metered and filled into cans on the automatic filling line. The valve is installed and tightened, and the propellant is filled. The amount of propellant is 35-45% of the weight of the silicone waterproof coating. After weighing and water bath testing, the nozzle is installed to obtain silicone aerosol coating for waterproofing precision instruments.

[0017] Compared with the prior art, the beneficial effects of the present invention are reflected in: This invention employs a first solvent and a second solvent with different volatility properties. The first solvent evaporates relatively quickly, promoting rapid film formation after spraying; the second solvent evaporates more slowly, providing a more moderate evaporation characteristic, which is beneficial for improving the self-leveling and film quality of the microfilm after spraying, reducing surface micropore defects caused by excessively rapid evaporation, and forming a good waterproof layer.

[0018] This invention utilizes the synergistic effect of fluoroorganosilicon and organosilicon-acrylate resin as film-forming agents, combined with leveling and release agents to form a waterproof coating that possesses both long-lasting waterproofing and peelability. Used for the protection of precision instruments, the coating can be peeled off after a certain protection period, leaving no residual contamination on the instrument surface. This invention's aerosol coating is a low-viscosity, transparent liquid that can be directly sprayed onto instrument surfaces to form a film, or sprayed and then wiped to form a micron-level transparent waterproof coating, achieving complete coverage. This greatly facilitates the maintenance of precision instruments in humid areas. The formed waterproof coating possesses waterproof, dustproof, corrosion-resistant, and self-cleaning properties. The water contact angle of the waterproof coating remains above 120º over a long period, protecting precision parts from moisture and corrosive gases. Its use does not affect the surface appearance or feel of the precision instrument. Detailed Implementation

[0019] The following detailed experiments further illustrate this application. All raw materials used in this application are commercially available. The silicone-acrylate resin and release agent are self-made. The filling process utilizes a Class 100,000 cleanroom automated filling line. All raw materials and process preparation materials must be stored in sealed containers to prevent volatilization, dust contamination, and moisture absorption. The entire line is designed with explosion-proof and static electricity elimination devices to reduce safety risks.

[0020] Preparation of organosilicon-acrylate resin: Mix 3 kg of vinyl-terminated polydimethylsiloxane, 3 kg of butyl acrylate and 1 kg of methyl methacrylate evenly, add 3 kg of toluene and heat to 90°C in a sealed container, stir slowly and add 0.14 kg of initiator benzoyl peroxide to initiate free radical copolymerization, keep the reaction at the temperature for 2.5 h, and purify by distillation to obtain organosilicon-acrylate resin.

[0021] Preparation of the release agent: Mix 1 kg of spherical nano-silica with a particle size of 10-100 nm with 0.035 kg of KH570 and stir at 100 °C for 3 h to obtain the release agent.

[0022] Example 1 (1) Dissolve 0.4 kg of tridecafluorooctyltriethoxysilane (KH-F823, provided by Guangzhou Longkai Chemical Co., Ltd.) in 3 kg of the first solvent ethyl acetate and stir evenly to obtain material 1; dissolve 0.2 kg of organosilicon-acrylate resin in 2 kg of the second solvent butanol and stir evenly to obtain material 2; mix material 1 and material 2 and add 0.1 kg of peeling agent and 0.05 kg of organosilicon polyether copolymer (DOWSIL™57, Dow Chemical), ultrasonically disperse for 30 min, and filter through a 5 µm microporous membrane to obtain organosilicon waterproof coating; (2) The silicone waterproof coating is metered and filled into cans on the automatic filling line. The valve is installed and tightened, and the propellant HFC-134a is filled. The amount of HFC-134a is 45% of the weight of the silicone waterproof coating. After weighing and water bath testing, the nozzle is installed to obtain silicone aerosol coating for waterproofing precision instruments.

[0023] Example 2 (1) Dissolve 0.5 kg of heptadecafluorodecyltrimethoxysilane (KH-F1013, provided by Guangzhou Longkai Chemical Co., Ltd.) in 3.5 kg of the first solvent methyl ethyl ketone and stir evenly to obtain material 1; dissolve 0.3 kg of organosilicon-acrylate resin in 2.5 kg of the second solvent isopropanol and stir evenly to obtain material 2; mix material 1 and material 2 and add 0.1 kg of peeling agent and 0.08 kg of organosilicon polyether copolymer (DOWSIL™57, Dow Chemical), ultrasonically disperse for 30 min, filter through a 5 µm microporous membrane to obtain organosilicon waterproof coating; (2) The silicone waterproof coating is metered and filled into cans on the automatic filling line. The valve is installed and tightened, and the propellant butane is filled. The amount of butane is 40% of the weight of the silicone waterproof coating. After weighing and water bath testing, the nozzle is installed to obtain silicone aerosol coating for waterproofing precision instruments.

[0024] Example 3 (1) Dissolve 0.6 kg of heptadecafluorodecyltrimethoxysilane (KH-F1013, provided by Guangzhou Longkai Chemical Co., Ltd.) in 4 kg of the first solvent acetone and stir evenly to obtain material 1; dissolve 0.3 kg of organosilicon-acrylate resin in 3.0 kg of the second solvent acetylacetone and stir evenly to obtain material 2; mix material 1 and material 2 and add 0.12 kg of peeling agent and 0.1 kg of organosilicon polyether copolymer (DOWSIL™11, Dow Chemical), ultrasonically disperse for 30 min, filter through a 5 µm microporous membrane to obtain organosilicon waterproof coating; (2) The silicone waterproof coating is metered and filled into cans on the automatic filling line. The valve is installed and tightened, and the propane propellant is filled. The amount of propane filling is 35% of the weight of the silicone waterproof coating. After weighing and water bath testing, the nozzle is installed to obtain silicone aerosol coating for waterproofing precision instruments.

[0025] Comparative Example 1 The second solvent used is highly volatile ethyl acetate, otherwise it is the same as in Example 1.

[0026] Comparative Example 2 The first solvent used was butanol, which has low volatility; the rest was the same as in Example 1.

[0027] Comparative Example 3 The silicone-acrylate resin and the second solvent, butanol, were removed; otherwise, the process remained the same as in Example 1.

[0028] Comparative Example 4 The tridecafluorooctyltriethoxysilane and the first solvent ethyl acetate were removed; otherwise, the process remained the same as in Example 1.

[0029] Comparative Example 5 The silicone polyether copolymer was removed; otherwise, it remained the same as in Example 1.

[0030] Comparative Example 6 The stripping agent was removed; otherwise, it remained the same as in Example 1.

[0031] Comparative Examples 1-6 used the same formulation and packaging process as Example 1, and the raw material formulas are shown in Table 1.

[0032] Table 1: Formulation table (kg) for Example 1 and Comparative Examples 1-6

[0033] The aerosol coatings prepared in the above embodiments and comparative examples were subjected to performance tests, including hydrophobicity, water vapor barrier performance, and peelability.

[0034] (1) Hydrophobicity test of aerosol coatings: The aerosol coating was sprayed onto the surface of a polished low-carbon steel sheet with a thickness of 10-20 μm. After air drying at room temperature for 24 hours, the initial water contact angle was tested. Then, the sheet was immersed in water for 72 hours, and the water contact angle after immersion was tested, as shown in Table 2.

[0035] The aerosol coating was sprayed onto the surface of a polished low-carbon steel sheet with a thickness of 10-20 μm. After air drying at room temperature for 24 hours, the initial water contact angle was tested. Then, the sheet was soaked in 5% sodium chloride salt water for 72 hours, and the water contact angle after soaking was tested, as shown in Table 2.

[0036] Determination of water contact angle θ: 0 ° ≤ θ ≤ 90 ° is hydrophilic; 90 ° < θ ≤ 120 ° is hydrophobic; θ > 120 ° is well hydrophobic.

[0037] Table 2: Hydrophobicity Test of Aerosol Coatings

[0038] The aerosol coating of this invention can quickly level and form a uniform protective coating after spraying, without affecting the appearance. The formed coating has good hydrophobic properties and maintains a high water contact angle even after prolonged immersion in water or salt water. It can maintain its waterproof effect for a long time.

[0039] Comparative Example 1 uses a fast-evaporating solvent, with organosilicon-acrylate resin forming a film quickly, and tridecafluorooctyltriethoxysilane hydrolyzed to synthesize the film. However, it has many micropore defects, which affect the hydrophobicity and uniformity of the coating.

[0040] Comparative Example 2 uses a slow-evaporating solvent, which can easily become trapped in the film-forming coating, forming bubble defects and affecting the coating's appearance. This would negatively impact the appearance of the coating when used for instrument protection. Furthermore, the hydrophobicity would also be affected.

[0041] Comparative Example 3 uses only fluorinated organosilicon and highly volatile solvents to form a coating with micropores. Although the initial water contact angle is high, water molecules may penetrate into the micropores after soaking in water, resulting in a decrease in the water contact angle. Obviously, such water-permeable micropores pose a potential risk of corrosion to the instrument's waterproofing.

[0042] Comparative Example 4 uses only silicone-acrylate resin and a slow-evaporating solvent. The slow evaporation of the solvent makes it easy for it to be trapped in the film coating, forming bubble defects. Moreover, the hydrophobicity of the silicone-acrylate resin film is generally poor.

[0043] In Comparative Example 6, no stripping agent was used, resulting in a significant reduction in the hydrophobicity of the coating.

[0044] (2) Tests on the water vapor barrier properties and peelability of aerosol coatings: The aerosol coatings used in Comparative Examples 1-6 and Example 1 were sprayed onto the surface of easily rusted low-carbon steel polished sheets. The coating thickness was controlled at 30 μm. The sheets were left to stand at room temperature for 4 hours, followed by heat drying for 10 minutes. Seven batches of samples were placed in an environment with a relative humidity greater than 90%. Low-carbon steel is prone to rusting when exposed to water. Once moisture penetrates the coating, the waterproofing gradually fails, and rust appears. Samples were taken every week, and the coating was peeled off to observe the rust on the metal sheets and the peelability of the coating, as shown in Table 3.

[0045] Table 3: Test results of water vapor barrier performance of aerosol coatings

[0046] This invention provides an aerosol coating that forms on the surface of polished low-carbon steel sheets, effectively preventing water vapor penetration, preventing rust, and exhibiting good adhesion and peelability. The coating residue does not contaminate the appearance of the instrument. It utilizes a synergistic effect of fluorinated organosilicon and organosilicon-acrylate resin. The fluorinated organosilicon forms a rigid, highly adhesive coating through hydrolysis and condensation, while the organosilicon-acrylate resin forms a flexible and peelable coating. In Comparative Example 3, which uses only fluorinated organosilicon, the coating cannot be completely peeled off. The organosilicon polyether copolymer acts as a leveling agent, promoting coating uniformity and easy peeling. In Comparative Example 5, which does not contain the organosilicon polyether copolymer, the peelability of the coating is significantly reduced. In Comparative Example 6, which does not use a peeling aid, the coating cannot be completely peeled off, and the lack of nano-peeling aids to fill micropores allows water vapor to easily penetrate the coating, causing rust.

[0047] The applicant declares that the present invention, through the above embodiments, illustrates that the coating obtained by synergistic use of fluorinated organosilicon and organosilicon-acrylate resin, under the combined action of solvents with different volatility characteristics, leveling agents, and stripping agents, exhibits long-lasting water-blocking performance when used for waterproofing precision instruments, without affecting the appearance of the instruments. After protection, the coating can be peeled off without leaving any residue or contaminating the instruments. However, the present invention is not limited to the above embodiments. Those skilled in the art should understand that any improvements to the present invention based on the above technical concept, including equivalent functional substitutions of the raw materials, fall within the protection scope of the present invention.

Claims

1. A silicone aerosol type coating for waterproofing precision instruments, characterized by, The silicone aerosol coating comprises: a silicone waterproof coating and a propellant; the silicone waterproof coating, by weight, consists of: 4-6 parts fluorinated silicone, 2-3 parts silicone-acrylate resin, 30-40 parts first solvent, 20-30 parts second solvent, 1-1.5 parts peeling agent, and 0.5-1 part leveling agent; the propellant constitutes 35-45% of the weight of the silicone waterproof coating; wherein: The fluorinated organosilicon is at least one of trifluoropropylmethyldimethoxysilane, tridecylfluorooctyltriethoxysilane, tridecylfluorooctyltrimethoxysilane, and heptadecafluorodecyltrimethoxysilane; The organosilicon-acrylate resin is obtained by polymerizing vinyl-terminated polydimethylsiloxane with acrylate; The first solvent is one of methyl ethyl ketone, ethyl acetate, and acetone; The second solvent is one of acetylacetone, butanol, or isopropanol; The leveling agent is an organosilicon polyether copolymer; The stripping agent is nano-silica modified with silane coupling agent.

2. The silicone aerosol coating for waterproofing of precision instruments according to claim 1, characterized by, When the first solvent is ethyl acetate, the second solvent is butanol.

3. The silicone aerosol coating for waterproofing precision instruments according to claim 1, characterized by, The organosilicon-acrylate resin is obtained by polymerizing vinyl-terminated polydimethylsiloxane and acrylate in a mass ratio of 3:

4.

4. The silicone aerosol coating for waterproofing precision instruments according to claim 1, characterized by, The stripping agent is obtained by adding 3.5% of γ-methacryloyloxypropyltrimethoxysilane by mass of the total nano-silica to nano-silica and stirring the mixture at 90-100℃ for 3-5 hours.

5. The silicone aerosol coating for waterproofing precision instruments according to claim 4, characterized by, The nano-silica is selected from spherical nano-silica with a particle size of 10-100 nm. ‌ 6. The silicone aerosol coating for waterproofing precision instruments according to claim 1, characterized by, The organosilicon polyether copolymer is one of DOWSIL™11 and DOWSIL™57.

7. The silicone aerosol coating for waterproofing precision instruments according to claim 1, characterized by, The propellant is at least one of HFC-134a, propane, and butane.

8. The method for preparing the silicone aerosol coating for waterproofing precision instruments according to any one of claims 1-7, wherein the specific preparation method is as follows: (1) Dissolve the fluorinated organosilicon in the first solvent and stir evenly to obtain material 1; dissolve the organosilicon-acrylate resin in the second solvent and stir evenly to obtain material 2; mix material 1 and material 2, add peeling agent and leveling agent, ultrasonically disperse, filter, and obtain organosilicon waterproof coating; (2) The silicone waterproof coating is metered and filled into cans on the automatic filling line. The valve is installed and tightened, and the propellant is filled. The amount of propellant is 35-45% of the weight of the silicone waterproof coating. After weighing and water bath testing, the nozzle is installed to obtain silicone aerosol coating for waterproofing precision instruments.

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